Sunlight is divided into the ultraviolet ray, the visible ray and the infrared ray according to wavelength. Among them, the ultraviolet ray has beneficial aspects such as generating vitamin D in human bodies, and accordingly sunbathing has been recommended for a long period. However, accompanied by the destruction of the ozone layer in the stratosphere, the amount of ultraviolet rays reaching the earth surface has increased and a health damage caused by ultraviolet rays has become perceived as a problem. As the health damage, there are acute health damages such as sunburn and chronic health damages such as an increased risk of diseases, e.g., a skin cancer as a result of the accumulation of the damage over a long period. Thus, there is regarded as necessary a countermeasure that effectively blocks ultraviolet rays harmful to human bodies.
The ultraviolet ray is divided into three types, namely, UVA having a large wavelength (320 to 400 nm), UVB having a medium wavelength (280 to 320 nm) and UVC having a short wavelength (200 to 280 nm). However, UVC and a part of UVB (of 290 nm or less in wavelength) are absorbed in the ozone layer, and therefore they hardly reach the earth surface. The ratio of the ultraviolet rays in sunlight reaching the earth surface is around 6%, and of these ultraviolet rays, UVA accounts for around 90 to 95% and UVB for the rest. UVA penetrates deeply into the dermis and is regarded as a cause of wrinkles and sagging skin. In addition, UVA mutates melanin in the epidermis, resulting in darkened skin (suntan). On the other hand, UVB causes inflammation in the skin (sunburn) in a short period and a pigmentation after few days.
In order to prevent health damages caused by the exposure to ultraviolet rays, there are cosmetics generally used (for example, sunscreen creams) in which a component for preventing ultraviolet rays is blended. As the component preventing ultraviolet rays blended in such a type of cosmetics, there are organic ultraviolet absorbers that absorb ultraviolet rays and inorganic ultraviolet scattering agents that reduce the amount of ultraviolet rays reaching the skin by reflecting and scattering them. In many cases, these cosmetics are made up of a combination of multiple ultraviolet absorbers and ultraviolet scattering agents, making use of their characteristics.
The ultraviolet absorbers have their own absorbance wavelengths defined by the chemical structure of the substances and, as UVB absorbers, p-methoxycinnamic acid-2-ethylhexyl is widely used (see Patent Document 1). On the other hand, there are only few ultraviolet protective cosmetics commercially available at the present which contain an organic ultraviolet absorber with high absorptive capacities in the UVA wavelength range. In addition, 4-tent-butyl-4-methoxy-benzoylmethane (see Patent Document 2) used at the present as a UVA absorber has a UVA absorptive capacity, however, it has poor solubility in solvents used for general cosmetics, which turns out to be a large limitation to the preparation of cosmetics harmless to human bodies.
In addition, as an invention related to a p-alkoxycinnamic acid ester compound, in Patent Document 3, there is disclosed a thermosensitive recording material characterized in that its thermosensitive color developing layer contains at least one type of the cinnamic acid ester compounds of the following General Formula:
(where R1 is an alkyl group, an aralkyl group, an alkoxy group, a cyclohexyl group or a halogen atom; and R2 is an alkyl group, an aralkyl group, an alkoxy group, an acyl group, a cyclohexyl group, a hydrogen atom or a halogen atom), and there is described a p-methoxycinnamic acid p-ethylphenyl ester as a specific example of the cinnamic acid ester compounds. However, in Patent Document 3, there is not indicated that the described cinnamic acid ester compound is used as an ultraviolet absorber.
Further, Patent Document 4 discloses an ultraviolet absorber characterized by containing a diphenyl unsaturated compound, and as the diphenyl unsaturated compound, the compound (claim 3) of the following General Formula:
(where R1, R2, R3 and R4 are H or an alkoxyl group) is exemplified. An important aspect to be noted here is that the diphenyl unsaturated compound of the General Formula is a compound in which one of the two phenyl groups (A) has an Ac (acetyl group).    [Patent Document 1]
Japanese Patent Application Publication No. JP-A-2001-49233    [Patent Document 2]
Japanese Patent Application Publication No. JP-A-2004-51567    [Patent Document 3]
Japanese Patent Application Publication No. JP-A-3-297685    [Patent Document 4]
Japanese Patent Application Publication No. JP-A-7-26247